Ultratrace-level determination of glyphosate, aminomethylphosphonic acid and glufosinate in natural waters by solid-phase extraction followed by liquid chromatography-tandem mass spectrometry: performance tuning of derivatization, enrichment and detection.

A sensitive and robust analytical method for the quantification of glyphosate, aminomethylphosphonic acid (AMPA) and glufosinate in natural water has been developed on the basis of a derivatization with 9-fluorenylmethylchloroformate (FMOC-Cl), solid-phase extraction (SPE) and liquid chromatography followed by electrospray tandem mass spectrometry (LC-ESI-MS/MS). In order to maximize sensitivity, the derivatization was optimized regarding organic solvent content, amount of FMOC-Cl and reaction time. At an acetonitrile content of 10% a derivatization yield of 100% was reached within two hours in groundwater and surface water samples. After a twofold dilution the low acetonitrile content allowed solid-phase extraction of a sample of originally 80 mL over 200 mg Strata-X cartridges. In order to decrease the load of the LC column and mass spectrometer with derivatization by-products (e.g., 9-fluorenylmethanol FMOC-OH), a rinsing step was performed for the SPE cartridge with dichloromethane. Acidification of the sample and addition of EDTA was used to minimize complexation of the target compounds with metal ions in environmental samples. Due to the large sample volume and the complete FMOC-OH removal, limits of quantification of 0.7 ng/L, 0.8 ng/L and 2.3 ng/L were achieved in surface water for glyphosate, AMPA and glufosinate, respectively. The limits of detection were as low as 0.2 ng/L, 0.2 ng/L and 0.6 ng/L for glyphosate, AMPA and glufosinate, respectively. Surface water and ground water samples spiked at 2 ng/L showed recoveries of 91-107%.